Stators in electric motors and generators are usually equipped with stator coils.
Various winding techniques for stator coils, including needle techniques flyer techniques, hairpin techniques or pulling-in techniques, are known from the prior art. In hairpin technology, the winding head of the stator coil is constructed from coil segments, referred to as hairpins. These are conductors which are bent in a U shape and have two open ends. The central partial region, that is to say the closed end of the conductor, is referred to as a head. In hairpin technology, in particular the bending of the conductor at the closed end, that is to say at the head of the hairpin, is demanding and costly in terms of fabrication technology.
The coil segments are inserted with their open end regions into the grooves of the stator core. The closed ends of the coil segments project beyond the stator core and form a coil end in the form of the winding head.
The stator is used in an electric machine. In particular, in electric machines for mobile applications, such as for example for motor vehicles, there is the need to make the electric machine, and therefore the stator and the stator coil, as compact as possible. On the other hand, electric machines have losses as a result of the generation of heat both in the electrical sheet metal of the stator and in the stator winding. Although these heat losses can be reduced by selection of the sheet metal and configuration of the winding, thermal energy still needs to be dissipated even with optimum configuration. In order to prevent the temperature of the stator of the electric machine not exceeding the limiting temperature of the materials used, it is necessary to provide the stator with a cooling means.
Air cooling systems are known from the prior art. However, especially given the compact design of the stator and therefore small cooling surface said cooling systems are not very efficient, and are insufficient for cooling electric machines with a high power density.
Furthermore, fluid cooling systems are known from the prior art which provide stator cooling by means of a cylindrical outer jacket or by means a cylindrical inner jacket of the stator. Alternatively, fluid cooling systems are known in which the cooling fluid is conducted in pipes which are provided in the stator sheet metal. However, the integration of the pipes requires increased sheet metal cross section and therefore a greater stator volume.
Document US 2014/0115876 A1, which is incorporated by reference herein, discloses a coil segment and a corresponding method for manufacturing a coil segment, which method permits the volume of the stator to be reduced. For this purpose, a conductor bundle is firstly rotated in such a way that the individual conductors of the conductor bundle remain movable in a sliding fashion with respect to one another, are then pre-shaped and finally compressed by means of a compression molding method to form an essentially U-shaped coil segment. As a result of the rotation of the conductors, wherein the conductors remain movable in a sliding fashion with respect to one another, a conductor bundle is made available whose head has a comparatively small curvature radius. As a result, the part of the coil segment which projects out during the winding over the stator core, is reduced and therefore a stator with a comparatively small volume is made available.
A disadvantage of this invention is that although it permits a comparatively compact design of the stator, it does not provide a solution for efficient cooling of the stator in a way which saves installation space.